21193549991 has 2 divisors, whose sum is σ = 21193549992. Its totient is φ = 21193549990.

The previous prime is 21193549967. The next prime is 21193550009. The reversal of 21193549991 is 19994539112.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21193549991 - 2¹⁴ = 21193533607 is a prime.

It is a super-2 number, since 2×21193549991² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21193549961) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10596774995 + 10596774996.

It is an arithmetic number, because the mean of its divisors is an integer number (10596774996).

Almost surely, 2^21193549991 is an apocalyptic number.

21193549991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21193549991 is an equidigital number, since it uses as much as digits as its factorization.

21193549991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 787320, while the sum is 53.

The spelling of 21193549991 in words is "twenty-one billion, one hundred ninety-three million, five hundred forty-nine thousand, nine hundred ninety-one".